The invention relates to a field emission display device including a carbon nanotube film on cathode electrodes such that the film emits electrons under the influence of electric field between the cathode electrodes and grid electrodes.
FIG. 1 shows a conventional flat CRT. Line cathodes of tungsten as thermionic electron source are placed on a substrate. Scan electrodes and data electrodes are formed on either side of a glass plate having a plurality of through-holes at pixel locations. The electrodes with predetermined voltages applied thereto selectively pass the electrons emitted from the line cathode so that the electrons accelerate toward a screen and collide with phosphors coated on the inner surface of the screen. Here, the use of line cathodes limits the size of the display screen because the line cathodes of tungsten in a large display are more likely to vibrate and thus emission of electrons from becomes irregular. Moreover, heat generated from the line cathode may cause the electrode grid pate to deform resulting in unstable display images. It fails to teach the use of carbon nanotube as a source of electrons. In fact simple substitution of line cathodes with carbon nanotube is impossible since the former must be heated to emit electrons while the latter emit electrons when subjected to an electric field of a certain magnitude.
The use of carbon nanotube or the like has been suggested in a US patent to Debe (5,726,524). FIG. 3a of the patent teaches a patterned microstructure on a row electrode so that when voltage is applied between the row electrode and the column electrode electrons are emitted from the cathode to eventually hit the phosphor layer under the column electrodes. A drawback of this structure is that a high voltage potential can not be provided since the difference between the signal electrodes are well known not to exceed 300 V at best. In other words the maximum voltage difference is 600 V. This requirement is a cause of low brightness and short life span. Another FED structure shown in FIG. 3b uses gated electrodes and micro tip cathodes, to which switching signals are applied and electrons emitted are accelerated toward the phosphor screen by a high constant voltage of as much as 4KV potential at the anode. However, such an FED structure needs a complicated thin film process of repeatedly depositing material on a substrate and etching a predetermined pattern corresponding to pixels in order to grow gate electrodes and cathodes on a same substrate.
An objective of the present invention is to allow a large screen FED to have stable electron emission by a novel FED structure of carbon nanotube as a source of the electrons.
Another objective of the invention is to allow a large screen FED to be made without a complicated process of a prior art by separately providing a cathode layer and a grid layer.